Lingering La Nina Will Lower 2011 Corn Yield

Lingering La Nina Will Lower 2011 Corn Yield

What does the current La Nina weather pattern mean for crop prospects as we move into summer? It will have an impact on U.S. yield potential this year, especially for corn, says ISU's Elwynn Taylor.

The La Nina condition that's affecting this year's weather in Iowa and elsewhere is fading now in early June, but it will likely stay around at least until July and perhaps longer. And based on the adverse weather events that have occurred so far in 2011, including extensive flooding in several areas of the country and a high number of tornadoes, this year's La Nina will result in a U.S. corn yield average for 2011 that's below the trend line yield.

That's the latest update on the weather and La Nina situation from Elwynn Taylor, Iowa State University Extension climatologist.

A La Nina occurs when surface water temperatures in the central and eastern Pacific Ocean near the equator become cooler than normal. This affects weather patterns in the U.S. and other important growing regions in the world. Weather patterns that accompany a La Nina tend to be unfavorable for crop yields, while an El Nino has the opposite effect. When the cycle shifts from the La Nina to the El Nino phase, the ocean waters become warmer than normal and an El Nino usually results in weather patterns favorable for crop production.

Lingering La Nina will trim U.S. average corn yield in 2011

What does the currently lingering La Nina mean for U.S. crop prospects as we move into summer? It will have an impact on yield potential this year, for corn especially, says Taylor. "This La Nina we have now has been getting weaker in recent weeks," he notes. "But it's important to also note that this La Nina, since it began last fall, has been one of the strongest ever. So it is taking awhile for this La Nina to move down toward neutral."

The current La Nina ranks in the top two or three strongest La Nina events in history. La Nina and El Nino events have been recorded for 110 years or so. "Almost month-for-month we've been getting the same type of weather response from this current La Nina, extremely variable, not just here in the United States but in various places in the world," says Taylor.

He expects the highly variable weather that is accompanying the current La Nina to hang around into at least July or so, which will affect the 2011 crop growing season. "Looking back on this past winter and this spring, we've had a couple weeks that were a lot warmer than usual for that time of year, which were followed by a week or so that was colder than usual," says Taylor. "Then it went back the other way. The alternating extremes in temperature and precipitation are typical of a La Nina period."

Extreme variability in temperature, rainfall are typical of La Nina

Taylor adds, "This variable weather pattern of cold-warm, warm-cold from week to week has been occurring as long as this current La Nina has been going on, and we expect it to keep going on for at least into July this year."

When you have alternating extremes in temperature and rainfall, this isn't the best thing for crops. "Crops do a lot better when they are experiencing closer to the average weather rather than averaging the weather out by having extremes on both sides," says Taylor. "The extremes can be extreme cold, and extreme warm. Heat can bring stress quickly with the evaporation of available water in the soil for shallow rooted crops. Crops are shallow rooted because it's so wet."

The last two months have been on the wet side of usual, for most all of the Corn Belt, including Iowa. The eastern Corn Belt has been wettest. "Iowa is lucky this year that we were mostly planted in the state by mid-to-late May and the Iowa corn crop was up and out of the ground for the most part by the end of May," says Taylor. "In the eastern Corn Belt there were large areas that weren't planted yet by the end of May."

U.S. corn yield average will likely be below trend line this year

Does this lingering La Nina change Taylor's corn yield projection? Is the weather pattern in 2011 still following the La Nina weather pattern we had in 1974?

"Yes, it is still following 1974 and our yield projection doesn't change with this," he says. "The 90-day outlook the National Weather Service currently has issued for the Corn Belt this summer is a little more favorable for crops than the La Nina projection indicates. But both of these weather projections still indicate a below trend line U.S. yield for corn this year."

The National Weather Service weather forecast if it comes true would be just a little bit below the U.S. trend line yield projection of 162 bu. per acre, notes Taylor. That is, the national corn yield would average in the upper 150 bu. per acre range, say 158 bushels per acre approximately. But it would be only in the low 150 bushel to high 140 bushel per acre range if indeed the La Nina stays with us all the way through summer.

U.S. corn yield average could slip to 148 to 152 bushel range in 2011

If the U.S. corn yield stayed on the trend line in 2011, it would average 162 bushels per acre, Taylor adds. But if La Nina doesn't fade away and remains present through summer, and the U.S. corn yield ends up averaging only 148 to 152 bushels per acre, that would be very supportive of prices.

"Right now, La Nina is cutting this pretty close," he says. "We'll probably still have La Nina effects well into July. Even if La Nina ends at the end of June, we'll probably have a month of weather effects still occurring, before the atmosphere gets itself all cleaned up, you might say. So, a lingering La Nina does increase the risk of reducing the yield below the trend, which is right around 162 bu. per acre for the nation. I expect the U.S. average yield to be less than that in 2011."

Some news reports are stating that "La Nina is finished." However, Taylor's comment on that is, "It is clearly on the way out, but historically a strong La Nina like this one does not just leave with a whimper."

Chances of drought are less in 2011, but corn yield will still be down

People have always associated La Nina with potential for drought. Has the likelihood of drought this summer during the growing season lessened or is it still about the same?

"The likelihood of drought occurring in 2011 has lessened," says Taylor. "But remember, drought would cut 10% off the trend line yield. That would be cutting a full 16 bushels off of the 160 bushel trend. We don't think there's a high probability of having a severe drought in 2011. In fact it's a very low probability. But having a below trend line yield is still something that is likely to happen, as things look now."

So what's next? Taylor will be watching the activity of the Southern Oscillation Index to see where it stands at the end of June. If it's in neutral territory, that would mean an SOI of .8 or less. Neutral is .8, or if you are looking at the Australian measure, they move the decimal point. That is, the SOI would be under 8 to be neutral if you're getting your data from the Australian weather scientists, which is where most climatologists get the SOI data.

The SOI is the atmospheric pressure measurement associated with La Nina or El Nino. "The atmospheric pressure, the highs and lows, have direct impact on what's going on with weather, and that's why we use the SOI index rather than some of the other measures that are available," says Taylor. 

Don't expect the La Nina to shift to an El Nino this growing season

Final thought: If La Nina moves to neutral, it'll stay there for awhile and then it shifts to El Nino. An SOI of negative 8 indicates an El Nino situation.

"We don't expect the current La Nina situation to move to an El Nino this growing season," says Taylor. "El Nino is generally favorable for crop yields and a La Nina is generally unfavorable. It looks like at least into July, we'll be having a variable situation. Things would not be as good as they could be for corn and soybean crops in the Midwest, and there could be lots of problems elsewhere in the world as well, including tornadoes and so forth."

You can follow Elwynn Taylor's latest weather outlook and comments on the Web, just Google "Where's Elwynn?" On Twitter, go to twitter.com\ElwynnTaylor.

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